The present invention relates to warehousing systems and particularly to a system employing a mobile tier picking vehicle.
When selectively picking cartons from palletized loads of cartons, systems employing vacuum operated tier picking devices frequently require that the palletized loads be brought to a fixed tier picking location which includes a vacuum tier picking apparatus that selectively removes a tier of cartons from the palletized loads and transfers tier picked articles to a make-up pallet. The remaining cartons on the picking pallet must then be returned to storage by conventional load transferring means. U.S. Pat. No. 2,716,497 issued on Aug. 30, 1955 to E. A. Wahl et al., is representative of a system employing a typical fixed tier picking station. It is apparent that considerable inefficiency is inherent in the design of such systems since palletized loads must be taken out of storage, transferred to the picking station, returned to the storage area and then reinserted into storage
Recently, it has been suggested to incorporate tier picking mechanism on a stacker crane type of vehicle which can travel within an access aisle and remove palletized loads from storage and transfer tiers of articles from the removed picking pallet onto a make-up pallet also on the crane. The remaining articles on the picking pallet are then returned to storage. The stacker crane can progress along the aisle tier picking different articles until an entire pallet of tier picked articles has been loaded onto the make-up pallet and then transfer the make-up load to an output station for shipment or the like.
Although such a system represents an improvement over the fixed tier picking arrangement, the use of stacker cranes limits the through-put capacity of such a system since the vertically movable apparatus generally will take up an entire access aisle thereby prohibiting additional stacking cranes from operating in the aisle for picking entire or partial pallet loads. Additionally, when the make-up load is completed, the stacker crane and vacuum picker thereon must travel to a discharge location to transfer the make-up pallet thereby tying up the tier picking equipment during this period.
The warehousing system described in detail in a copending application entitled WAREHOUSING SYSTEM filed on July 17, 1972, Ser. No. 272,287 now U.S. Pat. No. 3,880,299 and assigned to the present assignee, incorporates a plurality of mobile transfer vehicles adapted to be dispatched into access aisles of a storage system and transfer unitized loads between the vehicle and storage bins along the aisle. In this system, the mobile transfer vehicles include means thereon for transferring loads between the vehicle and the storage location to facilitate the automatic storing and retrieving sequence of operation. One or more mobile vertical lifts travel across the ends of the access aisles to transport the mobile transfer vehicles to different aisle levels or aisles. As described in detail in the above identified application, which is incorporated by reference herein, such a system overcomes theh through-put limitations inherent in a stacker crane or other known warehousing systems.